1. Field of the Invention
The present invention relates to an optical pickup which is configured to allow a common object lens to illuminate a first light for performing information recording or information reproducing on a recording layer as a target and a second light different from the first light with respect to an optical recording medium, which includes a reference plane having a reflection film and the recording layer which is disposed at a layer position different from that of the reference plane and on which information recording is performed through mark formation according to light illumination, and to adjust a focus-aligned position of the first light passing through the object lens by changing collimation of the first light incident to the object lens. In addition, the invention relates to an optical drive apparatus having the optical pickup and a light illumination method.
2. Description of the Related Art
As an optical recording medium for recording/reproducing signals through light illumination, there have been widely provided the so-called optical discs such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc: registered trade mark).
As a next-generation optical recording medium with respect to the currently provided optical recording medium such as a CD, a DVD, and a BD, the inventor has already proposed the so-called bulk recording type optical recording medium disclosed in Japanese Unexamined Patent Application Publication No. 2008-135144 or 2008-176902.
Herein, the bulk recording is a technology for implementing a large recording capacity by performing multi-layer recording in a bulk layer (recording layer) 102 by performing laser light illumination with respect to an optical recording medium (bulk type recording medium 100) including, for example, at least a cover layer 101 and the bulk layer (recording layer) 102 as illustrated in FIG. 5 while sequentially changing a focus position.
With respect to the bulk recording, Japanese Unexamined Patent Application Publication No. 2008-135144 discloses a recording technology referred to as a micro-hologram method.
As illustrated later in FIG. 6, the micro-hologram method is mainly classified into a positive type micro-hologram method and a negative type micro-hologram method.
In the micro-hologram method, a so-called hologram recording material is used as a recording material for the bulk layer 102. As the hologram recording material, for example, a light-polymerized material such as a photopolymer or the like is widely known.
The positive type micro-hologram method is a method where two facing light flux (light flux A and light flux B) are focused at the same position to form a fine interference fringe (hologram) and the interference fringe is used as a recording mark as illustrated in FIG. 6A.
In addition, the negative type micro-hologram method illustrated in FIG. 6B is a method where, as the opposite concept of the positive type micro-hologram method, a pre-formed interference fringe is erased through laser light illumination and the erased portion is used as a recording mark.
FIGS. 7A and 7B are diagrams illustrating the negative type micro-hologram method.
In the negative type micro-hologram method, before a recording operation is performed, an initialization process for forming the interference fringe is performed on the bulk layer 102 in advance as illustrated in FIG. 7A. More specifically, as illustrated in the figure, the facing light flux C and D as parallel light are illuminated, so that the interference fringe are formed over the entire bulk layer 102.
In this manner, after the interference fringe is formed in advance by the initialization process, information recording is performed by forming the erase mark as illustrated in FIG. 7B. More specifically, in the state where the focus is aligned at an arbitrary layer position, the laser light illumination is performed according to the recording information, so that the information recording through the erase mark is performed.
In addition, as a bulk recording method different from the micro-hologram method, the inventor proposed a recording method of forming voids as the recording marks disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-176902.
The void recording method is a method of recording the voids in the bulk layer 102 by performing the laser light illumination with a relatively high power with respect to the bulk layer 102 which is configured with a recording material, for example, a light-polymerized material such as a photopolymer or the like. As disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, the reflective index of the void portions formed in this manner is different from those of other portions in the bulk layer 102, so that it is possible to increase light reflectance in the boundaries. Therefore, the void portions may function as the recording marks, so that the information recording through the formation of the void marks may be implemented.
Since the void recording method is the method of forming no hologram, when light illumination from one side is performed, the recording is completed. In other words, unlike the case of the positive type micro-hologram method, it is not necessary to focus two light flux at the same position so as to form the recording mark.
In addition, in comparison with the negative type micro-hologram method, there is an advantage in that the initialization process is unnecessary.
In addition, Japanese Unexamined Patent Application Publication No. 2008-176902 discloses an example where, at the time of performing the void recording, illumination of precure light before the recording is performed. However, although the illumination of precure light is omitted, the void recording is possible.
Although various recording methods described above are proposed for the bulk recording type (simply, referred to as a bulk type) optical disc recording medium, the recording layer (bulk layer) of the bulk type optical disc recording medium do not explicitly have a multi-layered structure where, for example, a plurality of reflection films are formed. In other words, in the bulk layer 102, a reflection film and guiding grooves are not provided for each recording layer unlike a general multi-layered disc.
Therefore, in the state of the structure of the bulk type recording medium 100 illustrated above in FIG. 5, since the marks are not yet formed at the time of recording, focusing servo or tracking servo may not be performed.
For this reason, in an actual case of the bulk type recording medium 100, a reference reflection plane (reference plane) having guiding grooves is provided as illustrated later in FIG. 8.
More specifically, the guiding grooves (position guides) are formed in a spiral shape or a concentric shape on the lower surface side of the cover layer 101 through formation of, for example, pits or grooves, and a selective reflection film 103 is formed thereon. Next, a bulk layer 102 is laminated through an adhesive material, for example, a UV cured resin or the like as an intermediate layer 104 in the figure on the lower layer side of the cover layer 101 where the selective reflection film 103 is formed in this manner.
Herein, through formation of the guiding grooves by the aforementioned pits, grooves, or the like, absolute position information (address information), for example, radial position information, rotational angle information, or the like is recorded. In the hereinafter description, the plane (in this case, the plane where the selective reflection film 103 is formed) where the guiding grooves are formed, and the absolute position information is recorded is referred to as a “reference plane Ref”.
In addition, after the bulk type recording medium 100 is formed to have the aforementioned medium structure, as illustrated later in FIG. 9, servo laser light (simply, referred to as servo light) as laser light for position control is illuminated on the bulk type recording medium 100 separately from the laser light (hereinafter, referred to as recording/reproducing laser light or simply recording/reproducing light) for recording (or reproducing) the marks.
As illustrated, the recording/reproducing laser light and the servo laser light are illuminated through a common object lens on the bulk type recording medium 100.
At this time, if the servo laser light reaches the bulk layer 102, the servo laser light may exert an adverse influence on the mark recording in the bulk layer 102. Therefore, in the bulk recording method in the related art, laser light having a wavelength band different from that of the recording/reproducing laser light is used as the servo laser light, and a selective reflection film 103 having a wavelength selectivity of reflecting the servo laser light and transmitting the recording/reproducing laser light is prepared as the reflection film which is formed in the reference plane Ref.
Based on this premise, operations at the time of recording the marks on the bulk type recording medium 100 are described with reference to FIG. 9.
First, when the multi-layered recording is performed on the bulk layer 102 where the guiding grooves or the reflection film are not formed, it is determined in advance which one of the layer positions the marks are to be recorded at in the depth direction of the bulk layer 102. The figure exemplifies the case where a total of five information recording layer positions L, that is, the first information recording layer position L1 to the fifth information recording layer position L5 are set as the layer positions (mark formation layer positions: referred as information recording layer positions) where the marks are formed in the bulk layer 102. As illustrated, the first information recording layer position L1 is the information recording layer position L of the uppermost portion, and after that, the information recording layer positions L are set in the lower layer side in the order of L2→L3→L4→L5.
At the time of recording in the bulk type recording medium where the marks are not yet formed, the focusing servo and the tracking servo based on the reflected light of the recording/reproducing laser light may not be performed with respect to each of the layer positions as a target in the bulk layer 102. Therefore, at the time of recording, the focusing servo control and the tracking servo control of the object lens are performed based on the reflected light of the servo laser light so that the spot position of the servo laser light tracks the guiding grooves on the reference plane Ref.
However, the recording/reproducing laser light is necessarily allowed to reach the bulk layer 102 which is formed on the lower layer side from the reference plane Ref in order to perform the mark recording, and the focus-aligned position is necessarily configured to be selected in the bulk layer 102. Therefore, in this case, the optical system is provided with a recording/reproducing light focusing mechanism for independently adjusting the focus-aligned position of the recording/reproducing laser light separately from the focusing mechanism for the object lens.
Herein, an overview of the optical system which includes the mechanism for independently adjusting the focus-aligned position of the recording/reproducing laser light, as an optical system for performing recording/reproducing with respect to the bulk type recording medium 100, is illustrated in FIG. 10.
In FIG. 10, the object lens illustrated in FIG. 9 is configured so as to be displaceable in the radial direction (tracking direction) of the bulk type recording medium 100 and the direction (focusing direction) of approaching/separating with respect to the bulk type recording medium 100 by a two-axis actuator as illustrated in the figure.
In FIG. 10, the mechanism of independently adjusting the focus-aligned position of the recording/reproducing laser light corresponds to the recording/reproducing light focusing mechanism (expander) in the figure. More specifically, the recording/reproducing light focusing mechanism is configured to include a fixed lens and a movable lens which is supported by a lens driving unit so as to be displaceable in the direction parallel to the optical axis of the recording/reproducing laser light. The collimation of the recording/reproducing laser light incident to the object lens in the figure is changed by driving the movable lens by the lens driving unit, so that the focus-aligned position of the recording/reproducing laser light is adjusted independently of the servo laser light.
In addition, as described above, since the recording/reproducing laser light and the servo laser light have different wavelength bands, in the case, the optical systems corresponding to the recording/reproducing laser light and the servo laser light may be configured so that the reflected lights of the recording/reproducing laser light and the servo laser light from the bulk type recording medium 100 are separated into the corresponding systems (in other words, the reflected lights are independently detected) by the dichroic prism in the figure.
In addition, in the case of considering the forward light, the dichroic prism has a function of combining the recording/reproducing laser light and the servo laser light in the same axis to be incident to the object lens. More specifically, in this case, as illustrated in the figure, after the recording/reproducing laser light is reflected through the expander by a mirror, the recording/reproducing laser light is reflected on the elective reflection plane of the dichroic prism to be incident to the object lens On the other hand, the servo laser light is transmitted through the elective reflection plane of the dichroic prism to be incident to the object lens.
FIG. 11 is a diagram illustrating the servo control at the time of reproducing in the bulk type recording medium 100.
At the time of performing the reproducing in the bulk type recording medium 100 where the mark recording has been already performed, the control of the position of the object lens based on the reflected light of the servo laser light is not necessary unlike the time of recording. In other words, at the time of reproducing, the focusing servo control and the tracking servo control of the object lens based on the reflected light of the recording/reproducing laser light may be performed with respect to the mark sequences as a target, which are formed at the information recording layer position L (referred to an information recording layer L in the case of the time of reproducing) as a reproducing target.
In the bulk recording method having the above configuration, the recording/reproducing laser light for performing the mark recording/reproducing and the servo light as the position control light are illuminated through the common object lens (combining the recording/reproducing laser light and the servo light on the same optical axis) on the bulk type recording medium 100, and after that, at the time of recording, the focusing servo control and the tracking servo control of the object lens are performed so that the servo laser light tracks the position guides of the reference plane Ref, and the focus-aligned position of the recording/reproducing laser light is separately adjusted by the recording/reproducing light focusing mechanism, so that the mark recording may be performed at the necessary position (in the depth direction and in the tracking direction) in the bulk layer 102 even in the case where the guiding grooves are not formed in the bulk layer 102.
In addition, at the time of reproducing, the focusing servo control and the tracking servo control of the object lens which are based on the reflected light of the recording/reproducing laser light are performed so that the focus position of the recording/reproducing laser light tracks the mark sequence which has been already recorded, so that the reproducing of the marks recorded in the bulk layer 102 may be performed.